Growth of world energy demand has prompted widespread research and development to identify alternative energy sources for satisfying such demand. One such promising alternative energy source is biofuel, which encompasses various types of combustible fuels that are derived from organic biomass. There is a strong desire to develop biofuels that are not only cost-competitive with fossil fuels but also offer environmental benefits and are renewable. One particular type of biofuel is biomass-derived pyrolysis oil. Biomass-derived pyrolysis oil can be burned directly as fuel for certain boiler and furnace applications. Biomass-derived pyrolysis oil can also serve as a potential feedstock in catalytic processes for the production of fuel in petroleum refineries. Biomass-derived pyrolysis oil has the potential to replace up to 60% of transportation fuels, thereby reducing the dependency on conventional fossil fuel and reducing its environmental impact.
Biomass-derived pyrolysis oil is produced through pyrolysis, including through recently-developed fast pyrolysis processes. Fast pyrolysis is a process during which organic biomass, such as wood waste, agricultural waste, etc., are rapidly heated to about 450° C. to about 600° C. in the absence of air using a pyrolysis reactor. Under these conditions, a pyrolysis vapor stream including organic vapors, water vapor, and pyrolysis gases is produced, along with char (which includes ash and combustible hydrocarbon solids). A portion of the pyrolysis vapor stream is condensed in a condensing system to produce a biomass-derived pyrolysis oil stream. Biomass-derived pyrolysis oil is a complex, highly oxygenated organic liquid that typically contains about 20-30% by weight water with high acidity (TAN>150).
The biomass-derived pyrolysis oil stream often contains metal ions that may be detrimental to downstream processing and usage of the biomass-derived pyrolysis oil. For example, the metal ions may form deposits on equipment, may result in poor emission performance of the biomass-derived pyrolysis oil, and/or may cause catalyst poisoning in downstream fuel upgrading processes. To remove metal ions from the biomass-derived pyrolysis oil stream, ion exchange beds are commonly employed downstream of the pyrolysis reactor.
The ion exchange beds are frequently regenerated to clean the metal ions therefrom, which serves to maintain consistent performance of the ion exchange beds. Water is typically employed for regenerating the ion exchange beds. However, biomass-derived pyrolysis oil is immiscible with water and will prevent proper regeneration of the ion exchange bed with water if the biomass-derived pyrolysis oil is still present in the ion exchange bed in high amounts. As such, before the ion exchange bed can be regenerated using water, the ion exchange bed is generally drained of the biomass-derived pyrolysis oil and flushed with an appropriate flushing stream that is miscible with the biomass-derived pyrolysis oil to remove most biomass-derived pyrolysis oil that remains in the ion exchange bed after draining. Ethanol, which is generally miscible with both water and the biomass-derived pyrolysis oil, is typically used to flush the biomass-derived pyrolysis oil from the ion exchange bed before regeneration with water. The ethanol used for flushing generally mixes with the biomass-derived pyrolysis oil after flushing and is processed with the biomass-derived pyrolysis oil in the downstream fuel upgrading processes. However, one common upgrading process for the biomass-derived pyrolysis oil is hydrotreating, which serves to reduce the oxygen content of the biomass-derived pyrolysis oil, thereby increasing fuel value of the biomass-derived pyrolysis oil. Hydrotreating biomass-derived pyrolysis oil that also includes ethanol converts the ethanol to ethane, which downgrades the fuel value of the biomass-derived pyrolysis oil.
Accordingly, it is desirable to provide processes and apparatuses that enable alternative options for flushing biomass-derived pyrolysis oil from ion exchange beds that will not downgrade the fuel value of the biomass-derived pyrolysis oil. It is also desirable to provide processes and apparatuses that still enable effective regeneration of the ion exchange bed with water through use of an appropriate flushing stream that is sufficiently miscible with water. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.